This invention relates to operation of valves, especially those used in difficult or corrosive locations or environments, such as marine valves.
Such valves usually require application of greater torque to initially open or initially close the valve than the further effort required to complete the opening or closing of the valve. Upon opening a fully closed valve, a relatively high torque is required to overcome the pressure differential across the valve, and to overcome the friction of the closed-valve parts. An increased torque is also required to initially move an open valve toward a closed position because a valve which has been open for some period of time often experiences a build-up of residues on the relatively movable parts of the valve which makes initial movement of those parts difficult.
In order to obtain a torque boost, it is usually necessary to slow the movement of the movable valve part with respect to the movement of the valve operator, which may be a hand wheel for valves which are manually operated. If there is a large reduction in speed of rotation of the movable valve part, so as to obtain an accompanying large input torque to the valve, the operator, such as the hand wheel, must be turned many times in order for the valve to be completely opened or completely closed.
Therefore, it would be advantageous to have an arrangement whereby a high torque can be initially applied to a valve during its initial opening or closing movement, followed by a lower ratio of speeds of the valve operator and valve parts, accompanied by a necessarily lower torque. In this way, high torque is available for overcoming the initial resistance of a valve to opening or closing, but a higher speed of opening or closing movement is available during the remainder of the opening or closing movement of the valve.
It is an object of the present invention to provide a torque booster for operating a valve which temporarily boosts the torque applied to a valve during initial opening and closing of the valve, but thereafter decreases the torque so that the speed ratio between the valve operator and the moving valve part is reduced, whereby the moving valve part more quickly responds to movement of the operator to complete opening or closing of the valve.
It is another object of the invention to provide such a torque booster including a gear reduction unit, and coupling means for temporarily operatively interposing the gear reduction unit between the valve operator and the valve during initial movement of the valve operator in a valve-opening or valve-closing direction, the coupling causing the gear reduction unit to be bypassed during further movement of the valve operator.
Additional objects and features of the invention are set forth in the following description, in which reference is made to the accompanying drawings.